Keyless Entry Going Out?

I apologize if this issue has already been covered, but I couldn't find the exact issue when I tried to search the site. Anyway...for the past few months, my keyless entry on my '05 Silverado has been getting worse and worse. It started by the range reducing more and more all the time. Now, it doesn't work at all half the time. I will have to mash the button over and over, and sometimes it will work. More often and not, I'm having to use my key.

Before anyone says, "Change the battery!", I already have. I got 2 remotes when I bought the truck. I used one and put the other on my spare key that hardly ever was used. When the issue first started, I replaced the battery in the remote I use all the time. That did nothing, so I switched to the other remote. That didn't change anything either. Just to make sure I covered all bases, I replaced the battery in that remote too, but nothing changed. To me, both remotes screwing up the same way, especially when one has hardly ever been used, is way too much of a coincidence for the problem to be with the remotes.

I guess my question is, where is the receiver on the truck that receives the signal from the keyless entry remotes? Is it possible it's dirty, or does it need to be replaced? Please help!! Thanks!!